SpaceTech’s EM of MERLIN frequency reference unit ready

Immenstaad, 27 September 2018: The German-French satellite MERLIN (Methane Remote Sensing LIDAR Mission) is a mission to observe the concentration of the greenhouse gas methane. In this cooperation between CNES and DLR, CNES signs responsible for the satellite bus, which is a Myriade Evolution, and DLR signs responsible for the instrument. The instrument on MERLIN is a pulsed high power LIDAR (Light Detecting and Ranging) operating precisely at the methane absorption lines at 1645.55 nm wavelength. The instrument emits two different wavelengths called ‘online’ and ‘offline’: Online means located in the absorption feature and offline beside it for reference purposes.

To enable the required emission wavelengths around 1645.5-1645.7 nm, a frequency reference unit (FRU) is part of the instrument on the satellite. The frequency reference unit contains a methane gas cell, several diode lasers (1064 nm and 1645 nm emission wavelength), a wavemeter and the associated control electronics including an FPGA for stabilizing the diode laser emissions and the high power laser pulse frequency to the methane cell and the wavemeter. The FRU is delivering its optical signals to the high power laser and measures their wavelengths and the ones of the high power laser pulses to MHz accuracy. In addition it performs the wavelength stabilization control loops for the internal diode laser and of the OPO of the high power laser.

One and a half years after the start phase C/D, SpaceTech GmbH delivered the CDR data package for the frequency reference unit to Airbus and DLR. The co-location took place on the 25th and 26th of July 2018 at the SpaceTech premises in Immenstaad, Germany. All RIDs have been closed and no showstoppers for the CDR have been found. The engineering model has been built and its final testing phase has started.

After the successful operation of the LRI on GRACE-FO in orbit, the development of the frequency reference unit is the next major C/D development activity for a laser-optical instrument at SpaceTech.

Key and driving requirements of the FRU are:

5 mW of optical output power at 1645 nm with a laser frequency accuracy and stability of 10 MHz

10 mW of optical output power at 1064 nm with less than 1 MHz linewidth

Measurement of every single transmitted pulse with a systematic error of less than 8 MHz

Controlling the cavity of the optical parametric oscillator in the main laser

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